1. Field of the Invention
This invention relates to a sheet material, hereinafter referred to as paper, having fireblocking and thermal insulating properties. In preferred embodiments, a paper according to the invention will prevent the propagation and burnthrough of a fire in aircraft according to the specifications in Title 14 of the U.S. Code of Federal Regulations Part 25, Parts VI and VII to Appendix F thereof, and in proposed changes to said Regulations, published September 2000 in the Federal Register, Vol. 65, No. 183, pages 56992-57022, herein incorporated by reference, and collectively referred to herein as the “FAA requirements.”
2. Description of the Related Art
Paper is made from fibers, and optionally other materials, dispersed in a liquid medium and deliquified, usually by placing on a screen and then applying pressure to make a sheet. Paper in the conventional sense is usually made from vegetable fibers, such as cellulose, dispersed in an aqueous medium usually with binder and filler, deposited on a rotary screen and rolled. However, “paper” as a broad term, as used herein, covers any fiber-based material in sheet form which can be made using papermaking technology.
Paper made of inorganic fibers tends to have lower tensile strength and lower flexibility than paper comprising large amounts of organic fibers. Partly, this is because the stiffer inorganic fibers have less ability to intertwine and form a stable sheet. Papers comprising organic fibers, such as cellulose, rely on strong hydrogen bonds to provide tensile strength to the sheet. These hydrogen bonds, formed as a result of the polar attraction between water and hydroxyl groups covering the surface of the cellulose fiber, are not possible with typical inorganic fibers (such as glass, silica and quartz). Making paper out of inorganic fiber materials having high heat and flame resistance, which retains flexibility and tensile strength, poses significant technical challenges.
U.S. Pat. No. 5,053,107 describes an organic-free ceramic paper for use in high temperature environments containing glass fiber as a binder. However, this paper lacks flexibility in general and becomes very brittle at temperatures above 1200° F., making it unsuitable for use in high temperature applications.
U.S. Pat. No. 5,567,536 discloses a porous paper including inorganic ceramic fibers with an inorganic silica fiber binder system that initially includes organic materials. The organics, which are present for strength in the forming process, are subsequently combusted out after the paper has been produced and prior to the end use application. This results in a weak paper with only about 5 grams per inch of tensile strength per pound of basis weight. Such a weak paper would be likely to tear apart or rip during handling if it were installed as a fire barrier in an aircraft fuselage.
U.S. Pat. No. 4,885,058 discloses a paper which includes inorganic fibers and organic fibers as a binding agent. The tensile strength of the materials disclosed is generally poor. Moreover, the cellulosic fiber content of these materials causes the paper to burn at relatively low temperatures.
U.S. Pat. No. 4,746,403 describes a sheet material for high temperature use also having water resistance. The sheet comprises a glass fabric mat embedded in a layered silicate material. Although “paper-like,” the sheet material is not prepared from a fibrous dispersion utilizing papermaking technology. The disclosed materials are not waterproof or impervious to water, but described as not substantially degrading in tensile strength when exposed to water.
U.S. Pat. No. 4,762,643 discloses compositions of flocced mineral materials combined with fibers and/or binders in a water resistant sheet. These products, made from swelled, layered flocced silicate gel materials, are stable to a temperature of approximately 350-400° C., however, at higher temperatures they begin to degrade, and they are not able to maintain structural stability above 800° C. The poor heat resistance of these materials makes them unsuitable for fireblocking applications.
All of the above mentioned patent disclosures are incorporated herein by reference. A solution to the varied technical problems described in these disclosures would represent an advancement in the art.